It is the function of pipette tip racks to organize disposable pipette tips in a manner for convenient tip placement on a pipette. Generally, such racks comprise a rigid base with vertical sides joined at contiguous edges and horizontally supporting a rigid pipette tip organizing tray having an array of pipette tip receiving holes extending through a top surface of the tray. Alternatively, such tip racks comprise a rigid tray which includes support sides or legs and a flat top surface containing an array of holes for receiving and supporting an array of pipette tips. In either case, the pipette tips are organized and held vertically by the array of holes for ease of access by a pipette. In this regard, a technician simply places a hand holdable pipette over the rack and lowers a distal end of the pipette into a proximal or upper end of a vertically oriented pipette tip and presses down to a affix the tip to the pipette. A similar operation is followed by a technician when connecting a plurality of tips to a multiple tip pipette. U.S. Pat. No. 4,676,377 describes a conventional pipette tip rack of the type just described and U.S. Pat. No. 4,779,467, describes a multiple tip pipette.
Once all tips are dispensed from the pipette tip rack, the rack may be discarded or reloaded with a new supply of pipette tips. U.S. Pat. Nos. 5,324,482 and 5,392,914, describe pipette tip packaging systems and refill packs for pipette tip racks for loading new supplies of pipette tips into reusable tip racks. With the packaging described in U.S. Pat. No. 5,324,482, a technician grasps and positions an alignment plate over a stack of trays containing replacement pipette tips. The technician presses downward on the alignment plate to engage a latching mechanism securing the alignment plate to an uppermost one of the pipette tip containing trays. The technician then moves the tip tray over an empty pipette tip rack, lowers the tip tray onto a top of the empty tip rack and depresses a release button disengaging the latching mechanism to allow the tip tray and the replacement pipette tips to drop into place in the tip rack. With the refill pack described in U.S. Pat. No. 5,392,914, the technician places a refill pack over the top of the reusable tip rack and, in one embodiment, simply presses down on the top of the pack to release a refill plate containing an array of replacement pipette tips into the empty tip rack.
In both the pipette tip packaging system and the refill pack described in the above-identified patents, a refill plate or tip tray carrying an array of replacement pipette tips lays on a top surface of a support tray of the pipette tip rack. When the technician desires to attach a pipette tip to a pipette, he follows the previously described method of placing a hand holdable pipette over the rack and lowering a distal end thereof into an upper end of a vertically oriented pipette tip, and pressing down to affix the tip to the pipette. As the technician lifts the pipette from the tip rack, the refill plate or tip tray tends to lift with the pipette tip from the top surface of the support tray of the tip rack. The frequency of such occurrences depends upon the downward force exerted by the technician in attaching the pipette tip to the hand holdable pipette and further depends upon whether hand holdable pipette is a single or multiple tip pipette, the occurrences being more common with multiple tip pipettes. To preclude such undesired lifting of the refill plate or tip tray from the support tray during the loading of pipette tips onto hand holdable pipettes, the commercial products corresponding to those illustrated and described in U.S. Pat. Nos. 5,324,482 and 5,392,914 have heretofore included hold down devices comprising conventional "arrow" clips positioned in diagonally opposite ones of the holes in the refill plate or tip tray containing the replacement pipette tips. Such arrow clips include an enlarged head for engaging the upper surface of the refill plate or tip tray. Shank portions of the arrow clips pass through the holes in the refill plate tray while enlarged lower ends of the arrow clip fit snugly into and extend slightly beyond corresponding holes in the support tray of the tip rack. Such arrow clips firmly affix and hold down the refill plates and tip trays on the top surface of the support tray of the tip rack.
Unfortunately, such arrow clips are inserted into holes which otherwise would contain replacement pipette tips. This of course limits the number of replacement pipette tips which may be contained in the packaging system and refill pack of the above described patents. Further, the use of the arrow clips requires the technician to manually secure the refill plate or tip tray to the tip rack. Of course, when it is desired to again refill the reusable tip rack with pipette tips, the technician must manually remove the arrow clips from the refill plate or tip tray to allow for a subsequent reloading of the tip rack in the manner previously described. Such manual attachment and removal operations are not only bothersome to the technician, but they may also lead to undesired contamination of the pipette tips by contact with the technician hands. Further, the arrow clips constitute additional components and material which must be disposed of after use which counteracts a major purpose of the packaging system and refill pack for pipette tip racks, namely, the minimizing of disposable waste.
Accordingly, there is a continuing need for a refill plate or tip tray hold down apparatus which (1) automatically secures the refill plate or tip tray to the top surface of the support tray of a reusable tip rack, (2) is readily disengaged when it is desired to remove the refill plate or tip tray from the tip rack, (3) does not occupy holes normally containing pipette tips and (4) does not add to disposable waste associated with the refill pack system. The present invention satisfies such needs.